1. Field of the Invention
The present invention relates to a sheet-supply device and an image forming device including the sheet-supply device.
2. Description of the Related Art
Recently, image forming devices such as laser printers, color ink jet printers, facsimile machines, and copy machines, are provided with a sheet-supply device that supplies one cut sheet at a time to an image forming section of the image forming device. Japanese Patent Application Publication Nos. 2001-106367 and 2002-60068 disclose sheet-supply devices that include a slanting tray plate, a separation plate, and a sheet-supply roller. A plurality of sheets is stacked on the tray plate. The sheet-supply roller is provided in confrontation with the tray plate and rotates to supply sheets downstream in a sheet-supply direction. The separation plate is disposed downstream from the tray plate in the sheet-supply direction. The separation plate has a separation slanted surface that extends in a direction that forms an obtuse angle with respect to the surface of the tray plate.
The sheet feed roller is in pressing contact with the uppermost sheet of the sheets stacked on the slanting tray plate. When the sheet feed roller is driven to rotate and a sheet is transported downward, the lower edge of the transported sheet abuts the separation plate, which intersects the sheet transport direction. The sheet advances with its lower end portion toward the guide direction until the sheet lower edge separates from the separation plate. In this way, single sheets can be separated from the sheet stack. The separated sheet is sent to an image forming portion of the image forming device by transport rollers disposed along the guide direction. After image forming portion forms and image on the sheet, the sheet is discharged from the image forming device.
It is preferable for the sheets stacked on the slanting tray plate to be supported with their lower edges abutting against the separation plate. Therefore, the separation plate is usually oriented with its upper surface (sheet abutting surface) flush with horizontal or tilted slightly so that the downstream end (with respect to the guide direction) is slightly above horizontal.
The sheet separation mechanism of a conventional sheet-supply device provides accurate separation during sheet feed. However, the load applied to the separation plate by the stacked sheets can vary. When too many sheets are stacked on the separation plate, the load on the separation plate can increase to the point that the sheets slide downstream across the surface the separation plate all at once. Further, when pliable sheets are set on the slanting tray plate, the sheets can bend so that their lower edges abut the separation plate at an acute angle of, for example, approximately 60 degrees, rather than a substantially 90 degree angle with provides better stability. In such a case, due to their pliability, a large number of sheets can slip over the separation plate to slide downstream all at once. If sheets slide together in this manner, it becomes impossible to support the sheets at a desired position, with a desired posture, and the like. Therefore, sheets do not reliably receive the separating action of the high-friction separation member, resulting in double feeding of sheets. This problem also occurs when the stacked sheets have a wide width.